Not Applicable.
Not Applicable.
(1) Field of the Invention
This invention relates to hydrogenfluorides of aminosilanols and their use. The hydrogenfluorides of aminosilanols are formed by the reaction of an aqueous solution of a fluorinated acid, preferably, hydrofluoric acid, with an aminoalkoxysilane. The hydrogenfluorides of aminosilanols are particularly useful in foundry binders, most particularly no-bake and cold-box phenolic urethane foundry binders.
(2) Description of the Related Art
One of the major processes used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry binder system that is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
Two of the major processes used in sand casting for making molds and cores are the no-bake process and the cold-box process. In the no-bake process, a liquid curing agent is mixed with an aggregate and shaped to produce a cured mold and/or core. In the cold-box process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. Phenolic urethane binders, cured with a gaseous tertiary amine catalyst, are often used in the cold-box process to hold shaped foundry aggregate together as a mold or core. See for example U.S. Pat. No. 3,409,579. The phenolic urethane binder system usually consists of a phenolic resin component and polyisocyanate component which are mixed with sand prior to compacting and curing to form a foundry binder system. Because the foundry mix often sits unused for extended lengths of time, the binder used to prepare the foundry mix must not adversely affect the benchlife of the foundry mix.
Among other things, the binder must have a low viscosity, be gel-free, remain stable under use conditions, and cure efficiently. The cores and molds made with the binders must have adequate tensile strengths under normal and humid conditions, and release effectively from the pattern. Binders, which meet all of these requirements, are not easy to develop.
Because the cores and molds are often exposed to high temperatures and humid conditions, it also desirable that the foundry binders provide cores and molds that have a high degree of humidity resistance. This is particular important for foundry applications, where the core or mold is exposed to high humidity conditions, e.g. during hot and humid weather, or where the core or mold is subjected to an aqueous core-wash or mold coating application for improved casting quality.
Phenolic urethane cold-box and no-bake foundry binders often contain a silane coupling agent and/or aqueous hydrofluoric acid to improve humidity resistance. See for example U.S. Pat. No. 6,017,978. The silane and hydrofluoric acid are typically added to the phenolic resin component of the binder.
However, the addition of the silane and free aqueous hydrofluoric acid in phenolic urethane binders often results in one or more problems. For instance, the hydrofluoric acid usually requires special handling procedures, particularly because it is known to etch vitreous materials, e.g. flow control sight tubes commonly used in pipe line systems to convey the binder from storage to its point of use. In the case of phenolic urethane no-bake binders, the use of the silane and hydrofluoric acid slows the chemical reaction, and thus increases the worktime of the foundry mix and the striptime of the core or mold. If a longer time is required for the sand mix to set, this negatively affects productivity. In the case of the phenolic urethane cold-box binders, a precipitate may form over time in the phenolic resin component, particularly when the solvent package for the phenolic resin component contains non-polar solvents. The formation of a precipitate is undesirable because it requires disposal and adversely affects the storage and performance of the binder.
All citations referred to under this description of the xe2x80x9cRelated Artxe2x80x9d and in the xe2x80x9cDetailed Description of the Inventionxe2x80x9d are expressly incorporated by reference.
This invention relates to certain hydrogenfluorides of aminosilanols and their use. The hydrogenfluorides of aminosilanols have the following structural formula: 
wherein:
(1) R1 and R2 are selected from the group consisting of H; alkyl groups, aryl groups, substituted alkyl groups, aryl groups, mixed alky-aryl groups; di- or triamino groups, amino alkyl groups, amino aryl groups, amino groups having mixed alky-aryl groups, and amino groups having substituted alkyl groups, aryl groups, mixed alky-aryl groups; aminocarbonyl groups; and alkylsilanol groups, preferably where at least one of the R1 and R2 groups is H and the other group is an unsubstituted alkyl group having 1-4 carbon atoms;
(2) n is a whole number from 1 to 3, preferably where nxe2x89xa71;
(3) n+m=3;
(4) p is a whole number from 1 to 5, preferably 2 to 3
(5) Ra is selected from the group consisting of alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups, mixed alkyl-aryl groups, preferably an unsubstituted alkyl group having from 1-4 carbon atoms;
(6) x is a number and is equal to 0.1 and 3 per nitrogen atom of the aminosilanol, and is preferably from 1 to 2.5 per nitrogen atom in the aminoalkoxysilane; and
(7) Yxe2x95x90HF or HF complex, which results from a compound that hydrolyzes to yield HF, for instance ammonium fluoride, ammoniumbifluoride, potassium bifluoride, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid, N,N-diisopropyl aminetris(hydrogenfluoride), N,Nxe2x80x2-dimethyl-2-imidazolidone-hexakis(hydrogenfluoride), preferably HF.
The compositions contain little or no free fluorinated acid. An unexpected advantage of the hydrogenfluorides of an aminoalkoxysilane is that they can be dried, packaged as a powder, transported, and then redissolved in a solvent at the site where they are used without loss of activity, even though they are hydrolysis products of aminoalkoxysilanes. This reduces or eliminates the handling problems associated with using fluorinated acids, such as hydrogen fluoride.
The hydrogenfluorides of aminosilanols are particularly useful in foundry binders, most particularly no-bake and cold-box phenolic urethane foundry binders. Phenolic urethane no-bake binders containing the hydrogenfluorides of aminosilanols have excellent humidity resistance, and this is achieved without substantial adverse effects on the reactivity of the binder. Phenolic urethane cold-box binders containing the hydrogenfluorides of aminosilanols also have excellent humidity resistance. In some cases, there is an additional advantage with respect to phenolic urethane cold-box binders. Certain phenolic urethane cold-box binders, which contain a diaminoalkoxysilane and non polar solvents, do not etch glass and show improved stability, i.e. they form little or no solid precipitate over an extended shelf life.
In contrast to the approaches shown in the prior art, where either HF or an aminosilane is used alone or in combination, the hydrogenfluorides of aminosilanols are the reaction product of a fluorinated acid (preferably HF), water, and aminoalkoxysilanes.
Not Applicable.
The detailed description and examples will illustrate specific embodiments of the invention and will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides those specifically disclosed.
The hydrogenfluorides of aminosilanols are the reaction products formed by the reaction of an aqueous solution of a fluorinated acid, either hydrofluoric acid or a fluorinated acid, which hydrolyzes to yield hydrofluoric acid, with a aminoalkoxysilanes. Preferably, the fluorinated acid is hydrofluoric acid, most preferably an aqueous solution of hydrofluoric acid, containing from 10 to 90 weight percent water, preferably 30-60 weight percent water. Other fluorinated acids that can be used are ammoniumfluoride, ammoniumbifluoride, potassiumbifluoride, tetrafluoroboric acid, hexafluorophosphoric acid, hexafluorosilicic acid, N,N-diisopropylaminetris(hydrogenfluoride), and N,Nxe2x80x2-dimethyl-2-imidazolidone-hexakis(hydrogenfluoride).
The aminoalkoxysilanes used to prepare the hydrogenfluorides of the aminosilanols have the following structural formula: 
wherein:
(1) R1 and R2 are selected from the group consisting of H; alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups; di- or triamino groups, amino alkyl groups, amino aryl groups, amino groups having mixed alky-aryl groups, and amino groups having substituted alkyl groups, aryl groups, mixed alky-aryl groups; aminocarbonyl; and alkoxysilane groups, where R1 and R2 can be the same or different and preferably where at least one of the R1 and R2 groups is H, and the other group is an unsubstituted alkyl group having 1-4 carbon atoms;
(2) n is a whole number from 1 to 3, preferably where nxe2x89xa71;
(3) n+m=3;
(4) p is a whole number from 1 to 5, preferably 2 to 3, and
(5) Ra and Rb are selected from the group consisting of alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups, preferably an unsubstituted alkyl group having from 1-4 carbon atoms, and can be identical or different.
Specific examples of aminoalkoxysilanes include 3-aminopropyldimethyl-methoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyl-triethoxysilane, 3-aminopropylmethyl-dimethoxysilane 3-aminopropylmethyl-diethoxysilane, N-(n-butyl)-3-aminopropyl-trimethoxysilane, N-aminoethyl-3-aminopropylmethyl-dimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureido-propyltriethoxysilane, N-phenyl-3-aminopropyl-trimethoxysilane, N-[(Nxe2x80x2-2-aminoethyl)-2-aminoethyl)]-3-aminopropyltrimethoxysilane and bis (3-trimethoxy-silylpropyl) amine.
The fluorinated acid and/or the aminoalkoxysilane may contain a polar solvent. Examples of polar solvents include, for example, water, methanol, ethanol, isopropanol and butanol; ethylene and propylene carbonate; ethylene glycol, propylene glycol, and ethers thereof; isophorone; tetrahydrofuran, dioxolane, 4-methyl dioxolane and 1,3-dioxepane. Typically the amount of solvent is from 0 to 1000, preferably 10 to 300 weight percent based on the weight of the aminoalkoxysilane.
The hydrogenfluorides of aminosilanols are prepared by reacting a fluorinated acid with the aminoalkoxysilane, typically in a plastic reaction vessel, preferably at temperatures of 10xc2x0 C. to 70xc2x0 C. and preferably at atmospheric pressure. The fluorinated acid is gradually added to the aminoalkoxysilane and the mixture is stirred gently. A modest exotherm results, and eventually a thin and clear liquid is obtained. The reaction product is tested for free fluorinated acid by bringing into contact with glass to see whether it etches the glass. The stoichiometrical ratio of fluorine of the fluorinated acid to nitrogen of the aminoalkoxysilane is from 0.1:1.0 to 3.0:1.0, preferably from 1.0:1.0 to 2.5:1.0.
The hydrogenfluorides of aminosilanols are particular useful additives for phenolic urethane foundry binders. These binders are well known in the art and commercially available. They contain a phenolic resin component and a polyisocyanate component, which are cured in the presence of a tertiary amine catalyst. The amount of hydrogenfluoride of an aminoalkoxysilane added to a phenolic urethane binder is from 0.1-10.0 weight percent, based on the weight of the phenolic resin component, preferably from 0.15 to 2.0 weight percent.
The phenolic resin component comprises a phenolic resole resin, which is preferably prepared by reacting an excess of aldehyde with a phenol in the presence of either an alkaline catalyst or a metal catalyst. The phenolic resins are preferably substantially free of water and are organic solvent soluble. The preferred phenolic resins used in the subject binder compositions are well known in the art, and are specifically described in U.S. Pat. No. 3,485,797, which is hereby incorporated by reference. These resins, known as benzylic ether phenolic resole resins, are the reaction products of an aldehyde with a phenol. They contain a preponderance of bridges joining the phenolic nuclei of the polymer, which are ortho-ortho benzylic ether bridges. They are prepared by reacting an aldehyde and a phenol in a mole ratio of aldehyde to phenol of at least 1:1 in the presence of a metal ion catalyst, preferably a divalent metal ion such as zinc, lead, manganese, copper, tin, magnesium, cobalt, calcium, and barium.
The phenols use to prepare the phenolic resole resins include any one or more of the phenols which have heretofore been employed in the formation of phenolic resins and which are not substituted at either the two ortho-positions or at one ortho-position and the para-position. These unsubstituted positions are necessary for the polymerization reaction. Any of the remaining carbon atoms of the phenol ring can be substituted. The nature of the substituent can vary widely and it is only necessary that the substituent not interfere in the polymerization of the aldehyde with the phenol at the ortho-position and/or para-position. Substituted phenols employed in the formation of the phenolic resins include alkyl-substituted phenols, aryl-substituted phenols, cyclo-alkyl-substituted phenols, aryloxy-substituted phenols, and halogen-substituted phenols, the foregoing substituents containing from 1 to 26 carbon atoms and preferably from 1 to 12 carbon atoms.
Specific examples of suitable phenols include phenol, 2,6-xylenol, o-cresol, p-cresol, 3,5-xylenol, 3,4-xylenol, 2,3,4-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol. multiple ring phenols such as bisphenol A are also suitable.
The aldehyde used to react with the phenol has the formula RCHO wherein R is a hydrogen or hydrocarbon radical of 1 to 8 carbon atoms. The aldehydes reacted with the phenol can include any of the aldehydes heretofore employed in the formation of phenolic resins such as formaldehyde, acetaldehyde, propionaldehyde, furfuraldehyde, and benzaldehyde. The most preferred aldehyde is formaldehyde.
The phenolic resin used must be liquid or organic solvent-soluble. The phenolic resin component of the binder composition is generally employed as a solution in an organic solvent. The amount of solvent used should be sufficient to result in a binder composition permitting uniform coating thereof on the aggregate and uniform reaction of the mixture. The specific solvent concentration for the phenolic resins will vary depending on the type of phenolic resins employed and its molecular weight. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.
The polyisocyanate component of the binder typically comprises a polyisocyanate and organic solvent. The polyisocyanate has a functionality of two or more, preferably 2 to 5. It may be aliphatic, cycloaliphatic, aromatic, or a hybrid polyisocyanate. Mixtures of such polyisocyanates may be used. Also, it is contemplated that chemically modified polyisocyanates, prepolymers of polyisocyanates, and quasi prepolymers of polyisocyanates can be used. Optional ingredients such as release agents may also be used in the polyisocyanate hardener component.
Representative examples of polyisocyanates which can be used are aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4xe2x80x2-dicyclohexylmethane diisocyanate, and aromatic polyisocyanates such as 2,4xe2x80x2 and 2,6-toluene diisocyanate, diphenylmethane diisocyanate, and dimethyl derivates thereof. Other examples of suitable polyisocyanates are 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate, and the methyl derivates thereof, polymethylenepolyphenyl isocyanates, chlorophenylene-2,4-diisocyanate, and the like.
The polyisocyanates are used in sufficient concentrations to cause the curing of the phenolic resin when gassed with the curing catalyst. In general the polyisocyanate ratio of the polyisocyanate to the hydroxyl of the phenolic resin is from 1.25:1 to 1:1.25, preferably about 1:1. Expressed as weight percent, the amount of polyisocyanate used is from 10 to 500 weight percent, preferably 20 to 300 weight percent, based on the weight of the phenolic resin.
The polyisocyanate is used in a liquid form. Solid or viscous polyisocyanate must be used in the form of organic solvent solutions. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.
Those skilled in the art will know how to select specific solvents for the phenolic resin component, and in particular the solvents required in the polyisocyanate component. It is known that the difference in the polarity between the polyisocyanate and the phenolic resins restricts the choice of solvents in which both components are compatible. Such compatibility is necessary to achieve complete reaction and curing of the binder compositions of the present invention. Polar solvents of either the protic or aprotic type are good solvents for the phenolic resin, but have limited compatibility with the polyisocyanate. Aromatic solvents, although compatible with the polyisocyanate, are less compatible with the phenolic results. It is, therefore, preferred to employ combinations of solvents and particularly combinations of aromatic and polar solvents.
Examples of aromatic solvents include xylene and ethylbenzene. The aromatic solvents are preferably a mixture of aromatic solvents that have a boiling point range of 125xc2x0 C. to 250xc2x0 C. The polar solvents should not be extremely polar such as to become incompatible with the aromatic solvent. Suitable polar solvents are generally those which have been classified in the art as coupling solvents and include furfural, furfuryl alcohol, cellosolve acetate, butyl cellosolve, butyl carbitol, diacetone alcohol, and xe2x80x9cTexanolxe2x80x9d.
The solvent component can include drying oils such as disclosed in U.S. Pat. No. 4,268,425. Such drying oils include glycerides of fatty acids which contain two or more double bonds. Also, esters of ethylenically unsaturated fatty acids such as tall oil esters of polyhydric alcohols or monohydric alcohols can be employed as the drying oil. In addition, the binder may include liquid dialkyl esters such as dialkyl phthalate of the type disclosed in U.S. Pat. No. 3,905,934 such as dimethyl glutarate, dimethyl succinate; and mixtures of such esters.
Although not required when the hydrogenfluoride of an aminosilanol is used, the binder may also contain a silane (typically added to the phenolic resin component) having the following general formula: 
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are hydrocarbon radicals and preferably an alkyl radical of 1 to 6 carbon atoms and R is an alkyl radical, an alkoxy-substituted alkyl radical, or an alkyl-amine-substituted alkyl radical in which the alkyl groups have from 1 to 6 carbon atoms, and can be identical or different. The silane is preferably added to the phenolic resin component in amounts of 0.01 to 5 weight percent, preferably 0.1 to 1.0 weight percent based on the weight of the phenolic resin component.
When preparing an ordinary sand-type foundry shape, the aggregate employed has a particle size large enough to provide sufficient porosity in the foundry shape to permit escape of volatiles from the shape during the casting operation. The term xe2x80x9cordinary sand-type foundry shapes,xe2x80x9d as used herein, refers to foundry shapes which have sufficient porosity to permit escape of volatiles from it during the casting operation.
The preferred aggregate employed for ordinary foundry shapes is silica wherein at least about 70 weight percent and preferably at least about 85 weight percent of the sand is silica. Other suitable aggregate materials include zircon, olivine, aluminosilicate, sand, chromite sand, and the like. Although the aggregate employed is preferably dry, it can contain minor amounts of moisture.
In molding compositions, the aggregate constitutes the major constituent and the binder constitutes a relatively minor amount. In ordinary sand type foundry applications, the amount of binder is generally no greater than about 10% by weight and frequently within the range of about 0.5% to about 7% by weight based upon the weight of the aggregate. Most often, the binder content ranges from about 0.6% to about 5% by weight based upon the weight of the aggregate in ordinary sand-type foundry shapes.
The binder compositions are preferably made available as a two-package system with the phenolic resin component in one package and the polyisocyanate component in the other package. Usually, the phenolic resin component is first mixed with sand and then the polyisocyanate component is added. Methods of distributing the binder on the aggregate particles are well-known to those skilled in the art.
The foundry binder system is molded into the desired shape, such as a mold or core, and cured. Curing by the cold-box process takes place by passing a volatile tertiary amine, for example dimethylethylamine, dimethylpropylamine, dimethylisopropylamine, and preferably triethyl amine, through the shaped mix as described in U.S. Pat. No. 3,409,579. Curing by the no-bake process takes place by mixing a liquid amine curing catalyst into the foundry binder system, shaping it, and allowing it to cure, as described in U.S. Pat. No. 3,676,392. Useful liquid amines have a pKb value generally in the range of about 5 to about 11. Specific examples of such amines include 4-alkyl pyridines, isoquinoline, arylpyridines, 1-vinylimidazole, 1-methylimidazole, 1-methylbenzimidazole, and 1,4-thiazine. Preferably used as the liquid tertiary amine catalyst is an aliphatic tertiary amine, particularly 4-phenylpropylpyridine. In general, the concentration of the liquid amine catalyst will range from about 0.2 to about 10.0 percent by weight of the phenolic resin, preferably 1.0 percent by weight to 4.0 percent by weight, most preferably 2.0 percent by weight to 3.5 percent by weight based upon the weight of the phenolic resin.
The following abbreviations and components are used in the Examples:
The following abbreviations are used:
A-1160 an ureidoalkoxysilane manufactured by OSi Specialties, a business of Crompton Corporation.
A-187 an epoxy silane manufactured by OSi Specialties a business of Crompton Corporation.
BOS based on sand.
Dynasylan 1411 a diaminoalkoxysilane manufactured by Sivento, a subsidiary of Degussa-Huels Corp., and having the same chemical composition as A-2120.
ISOCURE(copyright) 372F/672 F Binder a phenolic urethane cold-box foundry binder manufactured by Ashland Specialty Chemical Company, a division of Ashland Inc.
PEP SETS 1670/2670 binder a phenolic urethane no-bake binder manufactured by Ashland Specialty Chemical Company, a division of Ashland Inc., cured with PEP SETand 3501 liquid tertiary amine curing catalyst
% RH relative humidity %.
Silquest A-2120 a diaminoalkoxysilane manufactured by OSi Specialties a business of Crompton Corporation, and having the same chemical composition as Dynasylan 1411.
ST striptime, used in connection with the no-bake process for core/mold-making, is defined as the time elapsed between mixing the binder components and the sand and placing the sand mix in a pattern, and when the foundry shape reaches a level of 90 on the Green Hardness xe2x80x9cBxe2x80x9d Scale Gauge sold by Harry W. Dietert Co.
WT worktime, used in connection with the no-bake process for core-making, is defined as the time elapsed between mixing the binder components and when the foundry shape reaches a level of 60 on the Green Hardness xe2x80x9cBxe2x80x9d Scale Gauge sold by Harry W. Dietert Co., Detroit, Mich.